This invention relates to metrological apparatus, and more particularly to apparatus of the type employed for automated optical inspection of manufactured objects, particularly in regard to the determination of precise dimensional measurements of such objects. Even more particularly this invention relates to an improved variable magnification optical system and associated video camera for accurately performing computerized image analysis and dimensional measurements of such objects.
Metrological apparatus of the type described normally includes a support for the object upon which dimensional measurements are to be made, and some means for precisely moving either the object or the associated video camera which is employed for recording or displaying a magnified image of the object that is being inspected. Such apparatus in addition to being able to perform measurements in a horizontal or X-Y plane, also may include autofocus means for determining heights of the object in the Z direction normal to the X-Y plane. In this manner such apparatus is capable of producing a full, three-dimensional inspection of the object.
Heretofore, as disclosed for example in U.S. Pat. No. 5,389,774, it has been customary normally to employ in a video inspection system of the type described a conventional zoom lens comprising multiple moving lens elements or lens groups to vary focal length, and to maintain focus. These moving elements tend to be very sensitive, thus making it extremely difficult to achieve precise repeatability in regard to magnification, location and focus. Moreover, typical such zoom lenses are not telecentric, so that the position of the object within the depth of focus significantly affects apparent size of the object, particularly at lower magnifications and at larger fields.
Although as disclosed in U.S. Pat. No. 4,743,771 video based inspection systems have been designed to move both the video camera and associated objective or imaging lens system in unison toward and away from the work that is being inspected, such systems do not enable satisfactory variation of the magnification of an image.
To obviate some of those problems heretofore encountered, it is an object of this invention to provide an improved video based inspection system which employs fixed optical elements in telecentric imaging lenses for effecting zoom-magnification of images.
Still another object of this invention is to provide an improved zoom-magnification system of the type described wherein magnification variation is achieved by moving the video camera relative to the imaging lenses, while in turn mounting both the camera and imaging lenses for movement as a unit in order to maintain proper focus of an object that is being inspected.
A further object of this invention is to provide an improved system of the type described wherein the video camera is connected via mechanical coupling means to an adjustable iris diaphragm, so that movement of the camera will provide automatic and proper adjustment of the aperture in the associated iris diaphragm thereby to synchronize diaphragm aperture and magnification with camera position.
Other objects of this invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings.